Recently, organic semiconductor devices represented by an organic thin-film transistor have attracted attention owing to characteristics such as saving of energy, low costs, and flexibility which inorganic semiconductor devices lack. The organic semiconductor device is composed of several kinds of materials such as an organic semiconductor active phase, a substrate, an insulating phase, and electrodes. Of these, an organic semiconductor active phase in charge of carrier movement of charges plays a primary role in the device. The performance of the organic semiconductor device is affected by the carrier mobility of an organic material constituting the organic semiconductor active phase.
As processes for preparing the organic semiconductor active phase, there are generally known a vacuum deposition process which is carried out by vaporizing an organic material at a high temperature under vacuum and a coating process wherein an organic material is dissolved in a suitable solvent and the solution is applied. In the coating process, the coating can be also carried out using a printing technology without using high-temperature and high-vacuum conditions. Accordingly, since a significant reduction of production costs of the device preparation can be achieved by printing, the coating process is a preferable process from an economical viewpoint. However, hitherto, there is a problem that it is increasingly difficult to form the organic semiconductor active phase from a material by the coating process as the performance of the material increases as an organic semiconductor device.
For example, it has been reported that a crystalline material such as pentacene has a high carrier mobility equal to amorphous silicon and exhibits the excellent organic semiconductor device properties (see, e.g., Non-Patent Document 1). Also, there has been reported an attempt to produce an organic semiconductor device by the coating process through dissolution of a polyacene such as pentacene (see Patent Document 1). However, since pentacene has a low solubility owing to its strong cohesiveness, high-temperature heating or the like conditions are necessary for applying the coating process. Furthermore, since a solution of pentacene is extremely easily oxidized with air, the application of the coating process involves difficulty from processing and economical viewpoints. Moreover, a self-assembling material such as poly(3-hexylthiophene) is soluble in a solvent and the preparation of an organic semiconductor device by coating has been reported. However, since the carrier mobility is one FIGURE lower than that of a crystalline compound (see, e.g., Non-Patent Document 2), there is a problem that the resulting organic semiconductor device shows a low performance.
Moreover, although pentathienoacene wherein thiophene rings are condensed exhibits an improved oxidation resistance as compared with pentacene, pentathienoacene is practically not a preferable material since carrier mobility is low and synthesis thereof requires many steps (see, e.g., Non-Patent Document 3).    Non-Patent Document 1: “Journal of Applied Physics”, (USA), 2002, vol. 92, pp. 5259-5263    Non-Patent Document 2: “Science”, (USA), 1998, vol. 280, pp. 1741-1744    Non-Patent Document 3: “Journal of American Chemical Society”, (USA), 2005, vol. 127, pp. 13281-13286    Patent Document 1: WO2003/016599